Abstract.— Leopard shark tag re- 

 covery data, obtained from a 1979-88 

 study in San Francisco Bay, were ana- 

 lyzed to determine temporal and geo- 

 graphic distribution of the tagged 

 population. Virtual population analy- 

 sis of the tag recovery data was used 

 to derive fishing mortality rates, 

 which in turn were used to obtain 

 yield-per-recruit and stock replace- 

 ment values, and to estimate the ef- 

 fect of management by size limit on 

 stock replenishment and yield per 

 recruit. 



Of the tagged population, 11% was 

 recovered by sport anglers and com- 

 mercial fishermen, and the distribu- 

 tion of recoveries indicates that leo- 

 pard sharks are mostly resident in 

 San Francisco Bay, although a por- 

 tion of the population moves out of 

 the Bay during fall and winter. An 

 unusually high number of recaptures 

 was made in 1983, a year of El Nino 

 conditions and high river run-off. 

 After obtaining mortality, yield, and 

 stock replacement values, it was pro- 

 posed that a viable management 

 strategy for the San Francisco Bay 

 leopard shark would be a size limit 

 of 100 cm or 40 inches to ensure 

 maintenance of the stock and pro- 

 vide a yield per recruit not too far 

 below a maximum. 



Leopard Shark Triakis semifasciata 

 Distribution, Mortality Rate, 

 Yield, and Stocl< Replenishment 

 Estimates Based on a Tagging 

 Study in San Francisco Bay 



Susan E. Smith 



Tiburon Laboratory, Southwest Fisheries Center 

 National Marine Fisheries Service, NOAA 

 3150 Paradise Drive, Tiburon, California 94920 

 Present address La Jolla Laboratory, Southwest Fisheries Center 

 National Marine Fisheries Service, NOAA, P O Box 271, La Jolla, California 92038 



Norman J. Abramson 



Tiburon Laboratory, Southwest Fisheries Center 

 National Marine Fisheries Service, NOAA 

 3150 Paradise Drive, Tiburon, California 94920 



Manuscript accepted 19 January 1990, 

 Fishery Bulletin, U.S. 88:371-381. 



Shark has now become a familiar item 

 at seafood counters and on restaurant 

 menus in the United States (Slosser 

 1987), while in the past these fish 

 were often discarded as trash fish, or 

 at best valued for fish meal or their 

 vitamin A-rich livers (Frey 1971). 

 California has seen the rise of four 

 new commercial elasmobranch fisher- 

 ies since the mid-1970s (Holts 1988), 

 and recreational shark fishing has 

 grown in popularity in California and 

 in other coastal states (Ristori 1987). 

 The relatively rapid increase in shark 

 harvesting has created a pressing 

 need for more biological information 

 to support management of targeted 

 species, particularly information re- 

 lating to population structure, mor- 

 tality and replenishment rates, and 

 degree of exchange between stocks. 

 Elasmobranchs may be particularly 

 vulnerable to exploitation, because 

 they are generally slow growing and 

 produce relatively few young, with 

 recruitment appearing to be largely 

 determined by parental stock size 

 (Holden 1977). 



The leopard shark Triakis semifas- 

 ciata is harvested both commercial- 

 ly and recreationally in California. It 



occurs along the coast from Baja Cali- 

 fornia, Mexico, to Oregon, and is 

 very common in northern California 

 bays (Squire and Smith 1977, Esch- 

 meyer et al. 1983). Its fairly large size 

 (maximum recorded is 180 cm; Kato 

 et al. 1967) and accessibility in near- 

 shore areas and bays probably con- 

 tribute to its appeal with anglers and 

 small-scale commercial boat opera- 

 tors. Reported commercial landings 

 in California since 1980 have ranged 

 from 18,199 kg (40,085 lbs) in 1980 

 to 45,994 kg (101,309 lbs) landed in 

 1983 (Table 1), with the San Francis- 

 co area contributing a large portion 

 of the catch. Recreational landings 

 are comparatively larger, judging 

 from estimates of landings compiled 

 by the U.S. Department of Com- 

 merce Pacific Coast Marine Recrea- 

 tional Fishery Statistics Survey (Table 

 2). Recorded commercial landings of 

 leopard sharks may be misleading, as 

 leopard sharks are often Itmiped with 

 other species under the general cate- 

 gory "shark, unspecified." Because 

 of this reporting bias, it is difficult to 

 determine the full extent of the com- 

 mercial harvest. Further, it should be 

 noted that reliable data for stratifica- 



371 



